The introduction of sulfur atoms onto target molecules is an important area in organic synthesis, in particular in the synthesis of pharmaceutical compounds, and a wide variety of sulfuration agents have been developed for thionation reactions over the past few decades. In this Focus Review, we collect and summarize the C-S bond-formation reactions that have been used to construct C-S bonds in natural products and pharmaceutical compounds.

Transfer of sulfur: from simple to diverse.

Use of Lawesson's reagent in organic syntheses.

The combination of P4S10 and hexamethyldisiloxane efficiently converts esters, lactones, amides, lactams, and ketones to their corresponding thiono derivatives. In the presence of elemental sulfur, 3-oxoesters are converted to dithiolethiones by this reagent. Yields are comparable to or superior to those obtained with Lawesson's reagent. The method has the advantage that reagent-derived byproducts may be removed by a simple hydrolytic workup or by filtration through silica gel, rather than by chromatography, as required for Lawesson's reagent.

Thionation with the reagent combination of phosphorus pentasulfide and hexamethyldisiloxane.

A new and improved method for the preparation of (PhPSe 2 ) 2 (Woollins reagent (WR), 1) is reported. Reaction of dichlorophenylphosphine with Na 2 Se, (prepared from the reaction of elemental selenium and sodium in liquid ammonia) gives WR with excellent purity, high yield and on a larger scale than was previously possible. Four novel phosphorus-selenium heterocycles, including a spirocyclic heterocycle exhibiting a four-membered P 2 SeC ring. were obtained from the reaction of WR with two reactive substrates (diphenylcyclopropenone and methyl phenylpropiolate). Useful selenocarbonyl and thiocarbonyl compounds were obtained from the reaction of both WR and Lawesson's reagent with diphenylcyclopropenone. All new compounds were characterised spectroscopically and three demonstrative X-ray structures are reported.

A New Synthesis of (PhPSe2)2 (Woollins Reagent) and Its Use in the Synthesis of Novel P–Se Heterocycles

Synthetic strategies for the preparation of 9,10-dihydro-9,10-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivatives are of special interest for polymer industry as well as academia involved in development of halogen-free flame retardant additives. In this work, various amino-DOPO derivatives (phosphonamidates) were synthesized by employing three different synthetic methods involving various chlorinating agents. The synthetic methods were compared with regards to purity and yield of the resulting amino-DOPO derivatives. The chlorinating agents that were used in this work are namely CCl4, trichloroisocyanuric acid and sulfuryl chloride. Some compounds, e.g., amine substituted DOPO derivative, could be synthesized using sulfuryl chloride with a yield >94% and a purity >99%. As proof of possible future industrial scale-up, up-scaling laboratory trials at the 500 g scale were also performed for two methods. The synthesized compounds were characterized for their melting point and thermal stability by using the...

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R.A. Cherkasov

Papers

Tetrahedron report number 186